Silvertone and silver colored would mean that although the item looks silver, the color is created without using any actual silver metal. Silver finish, depending on who is using that in their description, may mean something similar to silver colored, or may mean that a very thin layer of silver has been applied on top of some other metal base.
This is just my own personal preference, but I think that actual sterling silver jewelry is a much better value than something described as silvertone or silver colored, because the color will not wear away over time. Real silver jewelry may tarnish, but can be easily cleaned using a jewelry cleaner.
I hope you find this answer helpful!